The objective of the proposed research is to use feline and rat models of the human mucopolysaccharidoses (MRS) to understand the pathogenesis of these disorders, and to develop and evaluate therapeutic strategies for the treatment of their respective human counterparts. This proposal is a continuation of a longstanding collaboration between investigators at the University of Pennsylvania School of Veterinary Medicine and the Mount Sinai School of Medicine. Previously, our laboratories: 1) established breeding colonies for the animal models (cats with MPS I & VI, and rats with MPS VI), 2) characterized the clinical course and pathophysiology of each disease, 3) developed biochemical and molecular detection assays for the lysosomal enzymes which are deficient in these diseases, alpha-L-iduronidase (ID) and 4-sulfatase (4S), 4) isolated and expressed human, feline, and rat 4S and feline ID cDNAs, 5) constructed retroviral and adenoassociated viral vectors encoding human and feline 4S and human ID, 6) evaluated bone marrow transplantation (BMT) in MPS I and VI, 7) performed enzyme replacement therapy trials in MPS I, and 8) initiated hematopoietic progenitor cell gene marking experiments in MPS VI. Recently, we have 1) developed techniques to understand the bone and joint and neuronal pathogenesis, 2) explored protein expression in corneas in MPS I and VI cats, 3) performed neonatal retroviral gene therapy in MPS I and VI cats, and 4) begun enzyme replacement therapy studies with a fusion protein to target the CNS, The specific aims of the current proposal are to: 1) Continue to investigate the pathogenesis of the bone, joint, neuronal, and corneal lesions of MPS I and VI: 2) Continue to evaluate therapy in MPS I and VI using direct injection of modified enzyme into joints and several gene therapy approaches. These animal studies are designed to facilitate our understanding of disease pathogenesis and the development of therapy for the neuronopathic and non-neuronopathic forms of MPS.